1,3-butadiene, the demand for and value of which is gradually increasing as pertains to its use as an intermediate of many petrochemical products in petrochemical markets, is prepared using naphtha cracking, the direct dehydrogenation of n-butene, and the oxidative dehydrogenation of n-butene. However, the naphtha cracking process, which is responsible for 90% or more of 1,3-butadiene supplied to the markets, entails high energy consumption due to high reaction temperatures, and as well, is not a single process for producing 1,3-butadiene, and undesirably produces other fractions in surplus in addition to the 1,3-butadiene. Accordingly, this process is disadvantageous because investment in and management of a naphtha cracker cannot be optimized to satisfy the production demand for 1,3-butadiene, and thus, even though more novel naphtha crackers be utilized, the increasing demand for butadiene cannot be effectively satisfied. In addition, the direct dehydrogenation of n-butene is thermodynamically disadvantageous and is also unsuitable for commercial production of 1,3-butadiene because it is an endothermic reaction and thus requires high-temperature and low-pressure conditions to produce 1,3-butadiene at high yield [M. A. Chaar, D. Patel, H. H. Kung, J. Catal., vol. 109, pp. 463 (1988)/E. A. Mamedov, V. C. Corberan, Appl. Catal. A, vol. 127, pp. 1 (1995)/L. M. Madeira, M. F. Portela, Catal. Rev., vol. 44, pp. 247 (2002)].
In addition, the oxidative dehydrogenation of n-butene is a reaction for producing 1,3-butadiene through removal of two hydrogens from n-butene using oxygen as a reactant, and is thermodynamically advantageous because water, which is stable, is produced. Further, this process is commercially advantageous because 1,3-butadiene may be obtained at high yield even at lower reaction temperatures than direct dehydrogenation, without the need to additionally apply heat, thanks to exothermic properties. Furthermore, this process produces not only 1,3-butadiene but also water and therefore manifests energy reduction effects including additional production of steam. Hence, the oxidative dehydrogenation of n-butene for the production of 1,3-butadiene may be effective as a single production process able to satisfy the increasing demand for 1,3-butadiene. In particular, when a C4 raffinate-3 or C4 mixture including impurities, such as n-butane, used as an n-butene source, is directly used as a reactant without utilization of an additional process for separating n-butene, an advantage of adding high value to the C4 fractions produced in surplus may be realized. Specifically, the C4 raffinate-3 mixture, which is the reactant used in the present invention, is an inexpensive C4 fraction remaining after the separation of useful compounds, including 1,3-butadiene, isobutylene, 1-butene, etc., from a C4 mixture produced through naphtha cracking. More specifically, a first mixture remaining after extracting 1,3-butadiene from a C4 mixture produced through naphtha cracking is called raffinate-1, a second mixture remaining after extracting isobutylene from the raffinate-1 is called raffinate-2, and a third mixture remaining after extracting 1-butene from the raffinate-2 is called raffinate-3. Therefore, the C4 raffinate-3 is composed mainly of 2-butene (trans-2-butene and cis-2-butene), n-butane, and residual 1-butene.
According to the oxidative dehydrogenation of n-butene (1-butene, trans-2-butene, cis-2-butene) as mentioned above, n-butene reacts with oxygen, thus producing 1,3-butadiene and water. Although the oxidative dehydrogenation of n-butene has many advantages as a commercial process, it suffers because oxygen is used as the reactant in the above reaction, undesirably causing many side-reactions, including complete oxidation, etc. Thus, in order to efficiently improve the catalyst process, the development of catalysts having high selectivity for 1,3-butadiene while retaining high activity through control of the oxidation capability of the catalyst is of utmost importance. Examples of the catalysts known to date for use in the oxidative dehydrogenation of n-butene include ferrite-based catalysts [R. J. Rennard, W. L. Kehl, J. Catal., vol. 21, pp. 282 (1971)/W. R. Cares, J. W. Hightower, J. Catal., vol. 23, pp. 193 (1971)/M. A. Gibson, J. W. Hightower, J. Catal., vol. 41, pp. 420 (1976)/H. H. Kung, M. C. Kung, Adv. Catal., vol. 33, pp. 159 (1985)/J. A. Toledo, M. A. Valenzuela, H. Annendariz, G. Aguilar-Rios, Zapzta, A. Montoya, N. Nava, P. Salas, I. Schiffer, Catal. Lett., vol. 30, pp. 279 (1995)], tin-based catalysts [Y. M. Bakshi, R. N. Gur'yanova, A. N. Mal'yan, A. I. Gel'bshtein, Petroleum Chemistry U.S.S.R., vol. 7, pp. 177 (1967)], and bismuth molybdate-based catalysts [A. C. A. M. Bleijenberg, B. C. Lippens, G. C. A. Schuit, J. Catal., vol. 4, pp. 581 (1965)/Ph. A. Batist, B. C. Lippens, G. C. A. Schuit, J. Catal., vol. 5, pp. 55 (1966)/M. W. J. Wolfs, Ph. A. Batist, J. Catal., vol. 32, pp. 25 (1974)/W. J. Linn, A. W. Sleight, J. Catal., vol. 41, pp. 134 (1976)/W. Ueda, K. Asakawa, C.-L. Chen, Y. Moro-oka, T. Ikawa, J. Catal., vol. 101, pp. 360 (1986)/Y. Moro-oka, W. Ueda, Adv. Catal., vol. 40, pp. 233 (1994)/R. K. Grasselli, Handbook of Heterogeneous Catalysis, vol. 5, pp. 2302 (1997)].
Among these catalysts, the bismuth molybdate-based catalyst includes pure bismuth molybdate catalysts comprising bismuth and molybdenum oxide and multicomponent bismuth molybdate catalysts further comprising various metal components. Pure bismuth molybdate is present in various phases, and, in particular, three phases including α-bismuth molybdate (Bi2Mo3O12), β-bismuth molybdate (Bi2Mo2O9) and γ-bismuth molybdate (Bi2MoO6) are known to be useful as catalysts [B. Grzybowska, J. Haber, J. Komorek, J. Catal., vol. 25, pp. 25 (1972)/A. P. V. Soares, L. K. Kimitrov, M. C. A. Oliveira, L. Hilaire, M. F. Portela, R. K. Grasselli, Appl. Catal. A, vol. 253, pp. 191 (2003)]. However, a process of preparing 1,3-butadiene through the oxidative dehydrogenation of n-butene over a pure bismuth molybdate catalyst is limited in increasing the yield of 1,3-butadiene and is thus unsuitable for use as a commercial process [Y. Moro-oka, W. Ueda, Adv. Catal., vol. 40, pp. 233 (1994)]. As an alternative thereto, in order to increase the activity of the bismuth molybdate catalyst for the oxidative dehydrogenation of n-butene, attempts to prepare multicomponent bismuth molybdate catalysts comprising not only bismuth and molybdate but also other metal components have been made [M. W. J. Wolfs, Ph. A. Batist, J. Catal., vol. 32, pp. 25 (1974)/S. Takenaka, A. Iwamoto, U.S. Pat. No. 3,764,632 (1973)].
Some patents and literature have reported multicomponent bismuth molybdate catalysts for the oxidative dehydrogenation of n-butene. Specifically, many reports have been made of the oxidative dehydrogenation of 1-butene at 520° C. using a mixed oxide catalyst composed of nickel, cesium, bismuth, and molybdenum, resulting in 1,3-butadiene at a yield of 69% [M. W. J. Wolfs, Ph. A. Batist, J. Catal., vol. 32, pp. 25 (1974)], of the oxidative dehydrogenation of a C4-mixture including n-butane and n-butene at 470° C. using a mixed oxide catalyst composed of cobalt, iron, bismuth, magnesium, potassium, and molybdenum, resulting in 1,3-butadiene at a maximum yield of 62% [S. Takenaka, H. Shimizu, A. Iwamoto, Y. Kuroda, U.S. Pat. No. 3,998,867 (1976)], and of the oxidative dehydrogenation of 1-butene at 320° C. using a mixed oxide catalyst composed of nickel, cobalt, iron, bismuth, phosphorus, potassium, and molybdenum, resulting in 1,3-butadiene at a maximum yield of 96% [S. Takenaka, A. Iwamoto, U.S. Pat. No. 3,764,632 (1973)].
In the process for preparing 1,3-butadiene using the multicomponent bismuth molybdate catalyst disclosed in the above literature, 1,3-butadiene may be obtained at high yield when n-butene, in particular, 1-butene having relatively high reaction activity, is used alone as the reactant. In the case where a C4 mixture including n-butane and n-butene is used as a reactant, a multicomponent bismuth molybdate catalyst having a complicated composition of six or more metal components at a predetermined ratio should be used. That is, additional metal components must be continuously added to increase the activity of the catalyst, and thus the catalyst has a very complicated composition, undesirably resulting in a complicated catalyst synthesis route and a difficulty in ensuring reproducibility of catalyst preparation. In the above conventional techniques, as the reactant, only pure n-butene (1-butene or 2-butene) is used, or otherwise, a C4 mixture including n-butane and n-butene but having low n-butane content of less than 10 wt % is used. In the case where a C4 mixture having high n-butane content is used as the reactant, the yield of 1,3-butadiene is lowered. Because the C4 mixture which is easily obtainable as a result of actual petrochemical processes has high n-butane content, in order to apply the conventional catalyst to a commercial process, there is a need for an additional process for separating n-butene, inevitably remarkably decreasing economic efficiency. As a typical example, in a commercial process using a ferrite catalyst, a C4 mixture in which the n-butane content is maintained as low as less than 5 wt % is used as the reactant.
As mentioned above, the literature and patents regarding the catalyst and process for preparing 1,3-butadiene through the oxidative dehydrogenation of n-butene are characterized in that 1,3-butadiene may be obtained at high yield when using pure 1-butene or 2-butene as the reactant, and further, in the case where a C4 mixture having very high n-butene content is used as the reactant, a multicomponent bismuth molybdate catalyst having a very complicated combination of many metal components to increase the activity of the catalyst should be used, thus complicating the catalyst synthesis route and deteriorating the reproducibility of catalyst preparation. However, cases in which 1,3-butadiene is prepared from C4 fractions including C4 raffinate-3 or a C4 mixture having high n-butane content over a multicomponent bismuth molybdate catalyst having a simple composition of four metal components have not yet been reported.